In portable electronic devices, e.g. listening devices, that are turned on and off according to need, in particular battery driven devices, e.g. to conserve power, an account of absolute time elapsed from a given start time (including the time where the device has been turned off) may be difficult to estimate with an appropriate precision in the device without a (power consuming) real time clock circuit.
Some processing algorithms need an estimate of a real time elapsed, which is longer than a typical time of operation (uptime) of the device in question.
An uptime clock for measuring a time in which the device is in operation, and/or a power-up counter for counting a number of power-ups of device may be used to provide an estimate of a real time elapsed. An estimate of a real time elapsed may be based on the uptime multiplied by a predetermined factor, depending on the application of the device in question. Alternatively an estimate of a real time elapsed may be based on the number of power-ups multiplied by a predetermined time-value, depending on the application of the device in question, cf. e.g. US 2009/0154743 A1. These estimates are, however, subject to a substantial uncertainty due to the variance in use of the device from person to person and/or over time (e.g. from day to day).
US 2002/0044669 A1 describes a hearing aid adapted for detecting whether it is located in the immediate vicinity of an external transmitter with and thereby automatically choosing a hearing aid program depending on the external transmitter. In addition, the current time of day and the day of the week may influence the choice of the active hearing aid program.
US 2006/0023904 A1 describes a hearing aid adapted for emitting a voice signal to announce the current time of day, Preferably only the voice signal for the current time of day is saved in the hearing aid and to constantly update this voice signal by means of an external transmitter, preferably a remote controller. In this way, less memory space is thus required in the hearing aid for the time announcement.